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Baby on board!

Jo Dee Messina is expecting her second child with her husband of four years, businessman Chris Deffenbaugh.

"Our family is very excited. In a few months, Chris, Noah and I will be welcoming BABY #2!!!" the country music star, 41, announced on her Twitter Wednesday.

The "Unmistakable" singer and Deffenbaugh already have a two-year-old son, Noah Roger Deffenbaugh, together.